Analysis High-street socks'n'frocks chain Marks and Spencer is accused of quietly taking money from shoppers' contactless bank cards at the tills.
The accusations come from Radio 4's Money Box listeners, who called in to report that M&S had billed cards in purses and handbags over the air, unbeknownst to customers who had intended to pay for stuff another way.
It seems the money was unexpectedly taken from bank cards that can do pay-by-wave with compatible tills using Near Field Communications (NFC). One simply has to wave the card near the machine - within a few centimetres - for the transaction to take place over the air by radio wave.
But customers complained this was happening over a much greater distance with the tills that M&S recently installed in its UK stores.
The retail chain refunded the disputed payments - even those that went unnoticed until the customer's bank statement turned up weeks later - while pointing out that its NFC system was well tested prior to deployment. With a million transactions a month, one might expect more than couple of complaints if there was a significant problem.
The technology used by M&S is supplied by Visa. While neither company has responded to The Register's enquiries, we do know that several of the scenarios described by Money Box listeners should not be possible if the equipment is programmed to the NFC standard.
It's certainly possible for a till to debit the wrong card. However, doing so from several feet away beggars belief, in El Reg's opinion, as the induction coil that powers the NFC card has a very limited range: you effectively have to bonk your card against the machine.
However, one can imagine a wallet or purse being held beside an NFC reader in the same hand which is placing the preferred card onto the terminal, which could result in the wrong card being debited.
But the EMV (Europay, Mastercard, Visa) standard to which NFC terminals are supposed to conform requires the contactless circuit to be disconnected as soon as a chip'n'PIN card is slotted in. This is necessary as most chip cards also have NFC embedded, these days, and cards in the slot are perfectly positioned for the contactless reader; so the decision was made that the insertion of the card should indicate a preference for PIN.
One of the two callers who complained to Money Box said that a contactless transaction was made despite her debit card being in the Chip-and-PIN slot. Indeed, “Paula from London” claimed to have paid twice for the same goods, once using her PIN and once again using a contactless card which was 40cm away in her bag. M&S apparently refunded the money, but the BBC reckons other people may not have noticed.
Billing twice certainly shouldn't be possible. The process flow of a payment is well known, and the till shouldn't issue multiple receipts any more than it would accept two successive Chip-and-PIN payments for the same goods.
It is possible that the terminals used by M&S were hugely overpowered if they were reading cards at 40cm, or that they fail to implement the EMV standard properly. Equally, it's also possible that the tills are apparently running software which allows multiple billing for the same transaction. The two complaints to M&S, plus a similar complaint made to Pret a Manger, could well be the tip of an extensive iceberg.
That said, it's more likely that a customer placing a contactless card on a terminal accidentally had their wallet in the same hand, or an improperly inserted card resulted in the terminal contacting the NFC bank card in the shopper's purse instead.
Contactless payments are a bit scary, and one should probably keep an eye on one's credit card bills while the technology beds in, but on this particular scandal we'll side with Occam. ®